1. Field of the Invention
The present invention relates to a package structure of a sensor that measures a small flow rate, a pressure, a temperature, a concentration, a composition or the like of, e.g., a gas used in a semiconductor manufacturing apparatus, and to a flow sensor having the same.
2. Description of the Related Art
For example, as a flow rate measuring apparatus (a flow sensor) that detects a flow rate of a fluid, e.g., a gas used in a semiconductor manufacturing apparatus, there is a thermal type flow rate measuring apparatus that gives heat to a fluid and measures a temperature difference of the fluid at a predetermined position to measure a flow rate (see, e.g., Japanese Patent Application Laid-open No. H5(1993)-99722 (pp. 3-4, FIG. 1) and Japanese Patent Application Laid-open No. 2000-146652 (p. 2, FIG. 1)). Such a flow rate measuring apparatus is formed by bonding a sensor chip having a flow rate detecting device formed on a silicon substrate to a glass chip as a flow path chip that accommodates the flow rate detecting device and has a flow path (a groove) for a fluid flowing through the flow rate detecting device formed therein or to the silicon substrate.
Generally, in order to mount the flow rate measuring apparatus having the above-explained structure on a flowmeter or a flow rate controller, e.g., a mass flowmeter or a mass flow controller having a flow path body formed of a stainless member or the like, the flow rate measuring apparatus must be connected with the stainless member.
However, when a glass chip is bonded to a flow path body formed of a stainless member through, e.g., brazing, a difference in thermal expansion coefficient between both the members provokes distortion, thereby affecting sensor characteristics. Further, since a lead pattern must be pulled out to the outside of the flow path through a part of a bonded portion between the silicon substrate and the glass chip to take out an electrode, a countermeasure for maintaining strength or sealing properties of this portion is required. Furthermore, in a structure disclosed in Japanese Patent Application Laid-open No. 2000-146652 (p. 2, FIG. 1), since a part of a glass chip is constricted to take out an electrode, there is a problem of a reduction in strength of this constricted part.